Wow that's a lot of volume under the tank. What is the footprint of your stand? Does it take up all your room? I'm not opposed to a 40. What I dislike most about this 29 is no room for a refugium, and most of the vertical space is unused. Or does that mean I'm keeping my water level too low? Seems I'm having to top off every three days or the pump starts sucking air.I built mine out of a 40B. I love it. I traded coral for the glass baffles. Got taught how to cut it by my guy, then built my sump over the course of a few days. If I had to do it again... I may have gone bigger. But the tank is only 60 gallons so a 40B was a good sized sump and it left enough room in the stand to put a 5 gallon glass tank for my ATO.